This invention relates to control of engine fuel injectors and more particularly to a system and method for extending the operating range of the injectors.
It is well known in the engine art to supply fuel to engine cylinders or intake ports through fuel injectors that are fed with pressurized fuel at a constant pressure or pressure differential and have electrically controlled injection valves. The amount of fuel injected into the cylinders at each cycle is controlled by pulse width modulation of the electric valve control to vary the time the valve is open in accordance with the amount of fuel to be injected. As engine power outputs for automotive engines are increased, such as by supercharging or turbocharging, larger injectors may be required in order to provide the necessary amount of fuel for full power operation of the engine. In such cases, to operate the engine with the larger injectors at idle, the pulse width or injection time is reduced to the point where obtaining consistent fuel delivery from the injectors may become difficult. As a result, engine idle may be erratic or unstable. A system and method for extending the operating range of the fuel injectors is accordingly desired.
The present invention extends the operating range of fuel injectors fed by a pressurized fuel system of an engine by providing for operation of the fuel system at two or more different fuel pressure levels. For operating the injectors in a predetermined lower operating range, the fuel is controlled at a lower pressure, and when operating the system above the lower operating range, the fuel is controlled at a higher pressure. One or more intermediate ranges could be provided if desired. The higher pressure allows for additional fuel to be injected into the cylinders in order to provide increased output while operating within pulse width timing settings. When the desired engine output power is reduced, the system operates at a controlled lower fuel pressure. Thus, at higher loads for either naturally aspirated or supercharged (boosted) engines, additional fuel can be delivered by the injectors within their stable operating ranges. At lower loads and at idle, the lower fuel pressure allows the injectors to deliver smaller accurate fuel increments so that stable operation of the engine can be maintained within the operating range of the injectors
The invention is applicable to engines in general, including naturally-aspirated engines, but is particularly suitable for engines with power capabilities extended by supercharging, including turbocharging, wherein the output capability of engine cylinders is increased. In such cases, an increase in the size of the injectors may be minimized or even avoided by the use of the increased fuel pressure level for high power operation of the engine under turbocharged or supercharged conditions, and stable operation of the engine idle condition is easily accommodated while operating at the lower fuel pressure.
In a turbocharged engine, for example using two fuel pressure settings, the fuel pressure may be controlled by a three-way valve. In the lower power-operating range of the engine, the valve directs fuel to a low fuel pressure regulator, which returns excess fuel to the engine fuel tank. In the higher engine power-operating range, the valve is actuated to direct fuel to a high fuel pressure regulator and close off flow through the low pressure regulator so that the fuel pressure is increased to provide increased fuel injection from the injectors.
As an alternative, the fuel pressure can be controlled by a single valve at the inlet or outlet of the low pressure regulator. The valve is open to allow flow through the low pressure regulator which then controls the fuel pressure at a lower pressure level. To obtain a higher pressure, the valve is closed to block flow through the low pressure regulator, thus directing all the fuel flow through the high pressure regulator, which maintains fuel pressure at the desired higher level.
Control of the fuel pressure selection valve or device may be by any suitable means. In an automotive engine, an electronic control unit (ECU) or engine control module (ECM) may be used to initiate the valve setting although a suitable passive system might alternatively be applied, depending upon the engine control system capabilities
If desired, any other suitable control system for varying the fuel pressure may be utilized. Such alternatives would include a single pressure regulator with a variable pressure control actuated by any suitable electronic or pressure responsive means.
These and other features and advantages of the invention will be more fully understood from the following description of certain specific embodiments of the invention taken together with the accompanying drawings.